One month is a long time between home runs for most players, but for a slugger like Mike Napoli, it’s practically an eternity.Homerless, and with just one extra-base hit, in 90 plate appearances since a third-inning grand slam June 1 at Yankee Stadium, Napoli was absent from the Red Sox lineup in last night’s 2-1 win over the Padres at Fenway Park. It was a scheduled day off, according to manager John Farrell, who opted to give super-sub Mike Carp a rare start at first base.But considering Napoli’s injury history, including last winter’s diagnosis of a degenerative hip condition, it was worth wondering whether his power drought is health-related.

“We can’t pinpoint anything physically,” Farrell said. “Given what he has come through in the offseason, people might naturally think there’s something going on, which there isn’t.”Instead, Farrell pointed to Napoli’s swing. At his best, Napoli generates power with a more compact stroke that has produced an average of one homer per 16.5 at-bats. Lately, though, Farrell said his swing has gotten “long” and overcomplicated, with too many moving parts.Farrell also admitted he has considered dropping Napoli in the batting order — “There definitely has been some thought,” he said — after primarily keeping him in the No. 5 spot behind David Ortiz. For most of his career with the Angels and Rangers, Napoli has hit in either the No. 7 or 8 spots.